Method of fabricating dual damascene structure

ABSTRACT

A method of fabricating a dual damascene structure is described. A dielectric layer and a metal hard mask layer are sequentially formed on a substrate having thereon a conductive layer and a liner layer. The metal hard mask layer and the dielectric layer are patterned to form a via hole exposing a portion of the liner layer. A gap-filling layer is filled in the via hole, having a height of ¼ to ½ of the depth of the via hole. A trench is formed in the metal hard mask layer and the dielectric layer. The gap-filling layer is removed to expose the portion of the liner layer, which is then removed. A metal layer is formed filling in the via hole and the trench, and then the metal hard mask layer is removed.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an integrated circuit (IC) interconnectprocess, and more particularly to a method of fabricating a dualdamascene structure.

2. Description of Related Art

As the integration degree of semiconductor device is increased,multilevel metal interconnect is used widely. When the resistance of themetal of a metal interconnect is lower, the reliability and theperformance of the device are generally higher. Since copper has arelatively low resistance among various metal materials, it is suitablyused in a multilevel metal interconnect. However, copper is difficult toetch, so that a Cu-interconnect structure is usually formed with a dualdamascene process.

In a dual damascene process, a trench and a via hole are formed in adielectric layer, and then metal is filled in them to form a metal lineand a via plug. FIGS. 1A-1C illustrate a process flow of fabricating adual damascene structure in the prior art.

Referring to FIG. 1A, a dielectric layer 106 and a silicon nitride (SiN)layer 107 are formed over a substrate 100 with a metal layer 102 and aliner layer 104 thereon. Then, lithography and etching are performed toform, in the SiN layer 107 and the dielectric layer 106, a via hole 108that exposes a portion of the liner layer 104.

Referring to FIG. 1B, another lithography-etching process is conductedto form in the dielectric layer 106 a trench 110 connected with the viahole 108, and then the portion of the liner layer 104 exposed in the viahole 108 is removed.

Referring to FIG. 1C, a metal material is formed over the substrate 100,filling in the trench 110 and the via hole 108 and covering the SiNlayer 107. Then, a chemical mechanical polishing (CMP) step is conductedwith the SiN layer 107 as a polishing stop layer to remove the metalmaterial on the SiN layer 107 and form a dual damascene 112.

The above dual damascene process has some problems. Referring to FIGS.1A-1B, for the liner layer 104 in the via hole 108 is damaged by theetchant in the trench etching, the metal layer 102 is easily exposeddegrading the electrical properties. The SiN layer 107 and thedielectric layer 106 are also easily damaged by the etchant in thetrench etching so that the top corner of the trench 110 is rounded.Thus, bridging is easily caused between two adjacent dual damascenestructures 112, as shown in FIG. 2.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a method of fabricating a dualdamascene structure that can prevent rounding of the top corner of thetrench and thereby prevents bridging between two adjacent dual damascenestructures.

This invention also provides a method of fabricating a dual damascenestructure that can prevent the liner layer from being damaged by theetchant in the trench etching.

A method of fabricating a dual damascene structure is described. Asubstrate having a conductive layer and a liner layer thereon isprovided. A dielectric layer and a metal hard mask layer aresequentially formed on the liner layer and then patterned to form, inthe dielectric layer, a via hole that exposes a portion of the linerlayer. A gap-filling layer is filled in the via hole, having a height of¼ to ½ of the depth of the via hole, and then the metal hard mask layerand the dielectric layer are patterned to form a trench connected withthe via hole. The gap-filling layer is removed, and then the liner layerin the via hole is removed with the metal hard mask layer as a mask. Ametal layer is formed filling in the trench and via hole, and then thehard mask layer is removed.

According to the embodiments of this invention, the above gap-fillingmaterial may be a photosensitive polymer or a non-photosensitivepolymer.

In an embodiment, the gap-filling layer is formed by filling in the viahole a material layer having a height higher than a predetermined heightof ¼ to ½ of the depth of the via hole and then conducting etching-backto remove a portion of the material layer such that the remainingmaterial layer has the predetermined height.

In an embodiment, the steps of forming the trench and removing thegap-filling layer include forming a patterned photoresist layer on thehard mask layer, etching the hard mask layer and the dielectric layerwith the photoresist layer as a mask to form the trench and thenremoving the gap-filling layer and the photoresist layer simultaneously.In etching the metal hard mask layer and the dielectric layer, theetching selectivity of the dielectric layer to gap-filling layer mayrange from 0.5 to 1.5 as the dielectric layer is being etched. The stepof removing the gap-filling layer and photoresist layer simultaneouslymay utilize oxygen-plasma ashing.

In addition, the material of the metal hard mask layer may be selectedfrom titanium (Ti), tantalum (Ta), tungsten (W), titanium nitride (TiN),tantalum nitride (TaN), tungsten nitride (WN) and their combinations.

Another method of fabricating a dual damascene structure is describedbelow. A substrate having a conductive layer and a liner layer thereonis provided, a dielectric layer is formed on the liner layer, and then acap layer and a metal hard mask layer are formed on the dielectriclayer. The hard mask layer, the cap layer and the dielectric layer arepatterned to form, in the dielectric layer, a via hole that exposes aportion of the liner layer, and then a gap-filling layer is filled inthe via hole. A trench is formed in the dielectric layer connected withthe via hole, and then the gap-filling layer is removed. The liner layerin the via hole is removed with the metal hard mask layer as a mask, andthen a metal layer is formed filling in the trench and the via hole. Themetal hard mask layer is then removed.

In some embodiments of the above method, the above gap-filling materialmay be a photosensitive polymer or a non-photosensitive polymer.

In some embodiments of the above method, the gap-filling layer may havea height of ¼ to ½ of the depth of the via hole.

In some embodiments, the steps of forming the trench and removing thegap-filling layer include forming a patterned photoresist layer on themetal hard mask layer, etching the metal hard mask layer, the cap layerand the dielectric layer with the patterned photoresist layer as a maskto form the trench, and removing the photoresist layer and thegap-filling layer simultaneously. In etching the metal hard mask layer,the cap layer and the dielectric layer, the etching selectivity of thedielectric layer to the gap-filling layer may range from 0.5 to 1.5 asthe dielectric layer is being etched. The step of removing thegap-filling layer and photoresist layer simultaneously may utilizeoxygen-plasma ashing.

In some embodiments, the material of the cap layer may be silicon oxide(SiO), silicon nitride (SiN), silicon carbonitride (SiCN), siliconcarbide (SiC) or silicon oxy-nitride (SiON). The material of the metalhard mask layer may be selected from Ti, Ta, W, TiN, TaN, WN and theircombinations.

In some embodiments, the metal hard mask layer is formed on the caplayer. The step of removing the metal hard mask layer includes a CMPstep with the cap layer as a polishing stop layer.

In some embodiments, the metal hard mask layer is formed on the caplayer and an additional cap layer is formed on the metal hard masklayer. The additional cap layer is removed before the metal hard masklayer is removed. The step of removing the metal hard mask layer and theadditional cap layer includes a CMP step with the cap layer as apolishing stop layer.

In some embodiments, the cap layer is formed on the metal hard masklayer and is removed before the metal hard mask layer is removed.

Since a gap-filling layer is formed on the liner layer in the via holebefore the trench is formed, the liner layer is not damaged in thetrench etching so that the underlying conductive layer is not damagedand degraded. Meanwhile, the etching selectivity of the dielectric layerto the metal hard mask is very high, so that the trench top corner isnot rounded and bridging of two adjacent damascene structures isavoided.

In order to make the aforementioned and other objects, features andadvantages of the present invention comprehensible, a preferredembodiment accompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure in the prior art.

FIG. 2 illustrates the bridging between two adjacent dual damascenestructures with rounded trench top corners in the prior art.

FIGS. 3A-3F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to a first embodimentof this invention.

FIG. 4 illustrates the result of trench etching when the height of thegap-filling layer is larger than ½ of the depth of the via hole.

FIGS. 5A-5F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to a second embodimentof this invention.

FIGS. 6A-6F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to a third embodimentof this invention.

FIGS. 7A-7F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to a fourth embodimentof this invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIGS. 3A-3F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to the first embodimentof this invention.

Referring to FIG. 3A, a substrate 200 having a conductive layer 202 anda liner layer 204 thereon is provided, possibly being a semiconductorsubstrate like a bulk-Si substrate or an SOI substrate. The conductivelayer 202 may be a metal interconnect like a Cu line. The liner layer204 can prevent oxidation of the conductive layer 202, and may be an SiNlayer. A dielectric layer 206, such as a low-k layer with a dielectricconstant smaller than 4, is formed on the liner layer 204. A metal hardmask layer 210 is formed on the dielectric layer 206 through, forexample, CVD or sputtering, possibly including a material selected fromTi, Ta, W, TiN, TaN, WN and their combinations and having a thickness of50-300 Å. The thickness of the metal hard mask layer 210 is preferablyjust enough to avoid via-plug bridging, and the higher the etchingselectivity between the dielectric layer 206 and the metal hard masklayer 210 in the dielectric etching process is, the thinner the metalhard mask layer 210 can be. In some cases, an anti-reflection coating(ARC) 212 is further formed on the metal hard mask layer 210. Apatterned photoresist layer 214 is formed on the substrate 200, having avia-hole pattern 216 for forming a via hole.

Referring to FIG. 3B, the ARC 212, the hard mask layer 210 and thedielectric layer 206 are etched with the photoresist layer 214 as a maskto form, in the dielectric layer 206, a via hole 218 exposing a portionof the liner layer 204. In an example, the ARC 212 is etched with CF₄/O₂as an etching gas, the metal hard mask layer 210 etched with Cl₂/Ar asan etching gas, and the dielectric layer 206 etched with CF₄/Ar/N₂ orCHF₃/Ar/N₂ as an etching gas. The photoresist layer 214 is removed, andthen a gap-filling material 220 is filled in the via hole 218, possiblyincluding a polymer like a photosensitive polymer or anon-photosensitive one and formed with spin-on coating.

Referring to FIG. 3C, a portion of the gap-filling material 220 isremoved, such that the rest of the same is retained in the via hole 218as a gap-filling layer 220 a. The gap-filling layer 220 a preferably hasa height “h” of ¼ to ½ of the depth “H” of the via hole 218. The portionof the gap-filling material 220 may be removed through etching-back.Another patterned photoresist layer 222 is then formed over thesubstrate 200, having a trench pattern 224 for forming a trench later.

Referring to FIG. 3D, the ARC 212, the metal hard mask layer 210 and thedielectric layer 206 are etched with the patterned photoresist layer 222as a mask to form, in the dielectric layer 206, a trench 226 connectedwith the via hole 218.

In an example, the ARC 212 is etched with CF₄/O₂ as etching gas, withetching selectivities of 10-40 and 0.5-1.5 to the metal hard mask layer210 and the photoresist layer 222, respectively. The metal hard masklayer 210 is then etched with Cl₂/Ar as an etching gas, with etchingselectivities of 20-50 and 0.5-1.5 to the dielectric layer 206 and thephotoresist layer 222, respectively. The dielectric layer 206 is thenetched with CF₄/Ar/N₂ or CHF₃/Ar/N₂, as an etching gas, with etchingselectivities of 0.5-1.5, 5-20 and 20-50 to the gap-filling layer 220 a,the photoresist layer 222 and the metal hard mask layer 210,respectively. For the etching selectivity between the metal hard masklayer 210 and the dielectric layer 206 is very high, the profile of thetrench 226 can be well controlled. The etchants that can be used in thisinvention are not limited to the aforementioned. By selecting suitableetchants, the etching selectivities between different layers can becontrolled within desired ranges to improve the profile of the trench226 as well as to reduce the micro-loading effect caused by differentetching rates in dense-pattern areas and isolated-pattern areas.

The height “h” of the gap-filling layer 220 a is very important in thisinvention. If the height is smaller than ¼ of the depth “H” of the viahole 218, the gap-filling layer 220 a will be consumed in the etching ofthe trench 226, so that the liner layer 204 is exposed or is even etchedthrough to cause the conductive layer 202 to be damaged by the etchant.If the height is larger than ½ of the depth “H”, a dielectric fence 206a will form on the top corner of the via hole 218 after the trench 226is formed, as shown in FIG. 4, so that the subsequent metal filling isadversely affected.

Referring to FIG. 3E, the photoresist layer 222 and the gap-fillinglayer 220 a are removed. In some cases, the photoresist layer 222 andgap-filling layer 220 a are simultaneously removed with, for example,oxygen plasma ashing. The liner layer 204 in the via hole 218 isremoved, and a conductive layer 232 is formed on the substrate 200filling in the trench 226 and the via hole 218. The layer 232 is usuallyformed by forming a barrier layer 228 on surfaces of the trench 226 andthe via hole 218 and forming a metal layer 230 filling up 226 and 218.The material of the barrier layer 228 may be TiN or TaN, and the metallayer 230 may be a copper layer.

Referring to FIG. 3F, a portion of the conductive layer 232, the ARC 212and the metal hard mask layer 210 are removed, so that a conductivelayer 232 a is retained in the trench 226 and the via hole 218. Theremoval may be done through CMP.

Second Embodiment

FIGS. 5A-5F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to the secondembodiment of this invention. This process is similar to that in thefirst embodiment, except that after the dielectric layer is formed butbefore the metal hard mask layer is formed, a cap layer is formedcapable of serving as a polishing stop layer in the subsequent CMPprocess.

Referring to FIG. 5A, a structure including a substrate 200, aconductive layer 202, a liner layer 204 and a dielectric layer 206 isformed as in the first embodiment, while the materials and formingmethods of the layers may also be the same. A cap layer 206 is formed onthe dielectric layer 206 through, for example, CVD, possibly includingSiO, SiN, SiCN, SiC or SiON. A metal hard mask layer 210 is then formedon the cap layer 208, possibly in the same manner mentioned above. Insome cases, an ARC 212 is further formed on the metal hard mask layer210. A photoresist layer 214 is then formed on the substrate 200, with avia-hole pattern 216 for forming a via hole.

Referring to FIG. 5B, the ARC 212, the metal hard mask layer 210, thecap layer 208 and the dielectric layer 206 are etched with thephotoresist layer 214 as a mask to form, in the dielectric layer 206, avia hole 218 exposing a portion of the liner layer 204. The photoresistlayer 214 is removed, and a gap-filling material 220 is formed fillingin the via hole 218 possibly in the same manner mentioned above.

Referring to FIG. 5C, a portion of the gap-filling material 220 isremoved, such that the rest of the same is retained in the via hole 218as a gap-filling layer 220 a. The gap-filling layer 220 a preferably hasa height “h” of ¼ to ½ of the depth “H” of the via hole 218. The portionof the gap-filling material 220 may be removed with etching-back.Another patterned photoresist layer 222 is formed over the substrate200, having a trench pattern 224 for forming a trench in the dielectriclayer 206 later.

Referring to FIG. 5D, the ARC 212, the hard mask layer 210, the caplayer 208 and the dielectric layer 206 are etched with the photoresistlayer 222 as a mask to form, in the dielectric layer 206, a trench 226connected with the via hole 218. The etching selectivity of the layer206 to the gap-filling layer 220 a may range from 0.5 to 1.5.

Referring to FIG. 5E, the photoresist layer 222 and the gap-fillinglayer 220 a are removed. In some cases, the two layers 222 and 220 a aresimultaneously removed through, for example, oxygen plasma ashing. Theliner layer 204 in the via hole 218 is then removed, and a conductivelayer 232 is formed over the substrate 200 filling in the trench 226 andthe via hole 218, possibly in the same manner mentioned above.

Referring to FIG. 5F, a portion of the conductive layer 232, the ARC 212and the metal hard mask layer 210 are removed, so that a conductivelayer 232 a including a metal layer 230 a and a barrier layer 228 a isretained in the trench 226 and the via hole 218. The removal may be donethrough CMP, wherein the cap layer 208 can serve as a polishing stoplayer to prevent over-polishing of the dielectric layer 206 caused bydifferent polishing rates in dense-pattern areas and isolated-patternareas.

Third Embodiment

FIGS. 6A-6F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to the third embodimentof this invention. This process is similar to that in the firstembodiment, except that after the metal hard mask layer is formed butbefore the ARC is formed, a cap layer is formed on the metal hard masklayer to prevent the same from being exposed and causing contaminationin the step of removing the liner layer exposed in the via hole.

Referring to FIG. 6A, a structure including a substrate 200, aconductive layer 202, a liner layer 204, a dielectric layer 206 and ametal hard mask layer 210 is formed as in the first embodiment, whilethe materials and forming methods of the layers may also be the same. Acap layer 208 is formed on the hard mask layer 210, possibly in the samemanner mentioned above. In some cases, an ARC 212 is further formed onthe cap layer 208. A photoresist layer 214 is then formed on thesubstrate 200, with a via-hole pattern 216 for forming a via hole in thedielectric layer 206 later.

Referring to FIG. 6B, the ARC 212, the cap layer 208, the metal hardmask layer 210 and the dielectric layer 206 are etched with thephotoresist layer 214 as a mask to form, in the dielectric layer 206, avia hole 218 exposing a portion of the liner layer 204. The photoresistlayer 214 is removed, and a gap-filling material 220 is formed fillingin the via hole 218 possibly in the same manner mentioned above.

Referring to FIG. 6C, a portion of the gap-filling material 220 isremoved, such that the rest of the same is retained in the via hole 218as a gap-filling layer 220 a. The gap-filling layer 220 a preferably hasa height “h” of ¼ to ½ of the depth “H” of the via hole 218. The portionof the gap-filling material 220 may be removed through an etching-backstep. Another photoresist layer 222 is then formed over the substrate200, having a trench pattern 224 for forming a trench in the dielectriclayer 206 later.

Referring to FIG. 6D, the ARC 212, the cap layer 208, the metal hardmask layer 210 and the dielectric layer 206 are etched with thephotoresist layer 222 as a mask to form a trench 226 in connection withthe via hole 218. The etching selectivity of the dielectric layer 206 tothe gap-filling layer 220 a may range from 0.5 to 1.5.

Referring to FIG. 6E, the photoresist layer 222 and the gap-fillinglayer 220 a are removed. In some cases, the photoresist layer 222 andthe gap-filling layer 220 a are simultaneously removed through, forexample, oxygen plasma ashing. The liner layer 204 in the via hole 218is then removed, wherein the ARC 212 and the cap layer 208 can protectthe metal hard mask layer 210 from being exposed to cause contamination.A conductive layer 232 is then formed over the substrate 200 filling inthe trench 226 and the via hole 218, possibly in the same mannermentioned above.

Referring to FIG. 6F, a portion of the conductive layer 232, the ARC212, the cap layer 208 and the metal hard mask layer 210 are removed, sothat a conductive layer 232 a including a metal layer 230 a and abarrier layer 228 a is retained in the trench 226 and the via hole 218.The removal may be done through CMP.

Fourth Embodiment

FIGS. 7A-7F illustrate, in a cross-sectional view, a process flow offabricating a dual damascene structure according to the fourthembodiment of this invention. This process is similar to that in thethird embodiment, except that two cap layers are formed respectivelyunder and on the metal hard mask layer. Hence, the process is describedfor only the parts relating to the metal hard mask layer and the two caplayers, while the other parts of the process can be the same as in thethird embodiment.

Referring to FIG. 7A, the lower cap layer 207 is formed before the metalhard mask layer 210 is formed and the upper cap layer 208 after the sameis formed, wherein each of the two cap layers 207 and 208 may be formedas above. Referring to FIGS. 7A and 7B, in the etching process of thevia hole 218, with the photoresist layer 214 as a mask, the cap layer208, the metal hard mask layer 210 and the cap layer 207 aresequentially etched through. Referring to FIGS. 7C and 7D, in theetching process of the trench 226 with the photoresist layer 222 as amask, the cap layer 208, the metal hard mask layer 210 and the cap layer207 are also sequentially etched.

Referring to FIG. 7E, in the later step of removing the liner layer 204exposed in the via hole 218, the ARC 212 and the cap layer 208 canprotect the metal hard mask layer 210 from being exposed to causecontamination. Referring to FIGS. 7E and 7F, in a case where a portionof the conductive layer 232, the ARC 212, the cap layer 208 and themetal hard mask layer 210 are removed through CMP in the subsequentprocess, the cap layer 207 can serve as a polishing stop layer toprevent over-polishing of the dielectric layer 206 resulting fromdifferent polishing rates in dense-pattern areas and isolated-patternareas.

The present invention has been disclosed above in the preferredembodiments, but is not limited to those. It is known to persons skilledin the art that some modifications and innovations may be made withoutdeparting from the spirit and scope of the present invention. Therefore,the scope of the present invention should be defined by the followingclaims.

1. A method of fabricating a dual damascene structure, comprising:providing a substrate having a conductive layer and a liner layerthereon; forming a dielectric layer on the liner layer; forming a caplayer and a metal hard mask layer on the dielectric layer, wherein themetal hard mask layer is formed directly on the cap layer; forming anantireflection layer directly on the metal hard mask layer; patterningthe antireflection layer, the metal hard mask layer, the cap layer andthe dielectric layer consecutively to form, in the dielectric layer, avia hole that exposes a portion of the liner layer; filling agap-filling layer in the via hole and forming the gap-filling layer on atop surface of the antireflection layer; removing a portion of thegap-filling layer in the via hole and completely removing thegap-filling layer on the top surface of the antireflection layer;forming, in the dielectric layer, a trench connected with the via holeafter the step of removing a portion of the gap-filling layer in the viahole and completely removing the gap-filling layer on the top surface ofthe antireflection layer; removing the remaining gap-filling layer inthe via hole; removing the liner layer in the via hole with the metalhard mask layer as a mask; forming a metal layer filling in the trenchand the via hole; and removing the metal hard mask layer.
 2. The methodof claim 1, wherein the gap-filling layer comprises a photosensitivepolymer or a non-photosensitive polymer.
 3. The method of claim 1,wherein the remaining gap filling layer has a height of ¼ to ½ of adepth of the via hole.
 4. The method of claim 1, wherein the steps offorming the trench and removing the remaining gap filling layercomprise: forming on the antireflection layer a patterned photoresistlayer; etching the antireflection layer, the metal hard mask layer, thecap layer and the dielectric layer with the patterned photoresist layeras a mask to form the trench; and completely removing the patternedphotoresist layer and the gap-filling layer simultaneously.
 5. Themethod of claim 4, wherein in etching the antireflection layer, themetal hard mask layer, the cap layer and the dielectric layer, anetching selectivity of the dielectric layer to the gap-filling layerranges from 0.5 to 1.5 as the dielectric layer is being etched.
 6. Themethod of claim 4, wherein the step of completely removing thegap-filling layer and the photoresist layer simultaneously comprises anoxygen-plasma ashing step.
 7. The method of claim 1, wherein the metalhard mask layer comprises a material selected from Ti, Ta, W, TiN, TaN,WN and their combinations.
 8. The method of claim 1, wherein the step ofremoving the metal hard mask layer comprises a Chemical MechanicalPolishing step with the cap layer as a polishing stop layer.